Conventional lifter assemblies have included a top mounting plate by two pair of shafts located thereunder in order to extend and retract the mounting plate so as to lift a workpiece into a desired location. These lifter assemblies are used extensively in manufacturing operations, and find special utility in automotive manufacturing operations for lifting automotive workpiece components to facilitate the placement of the workpiece during the manufacturing operation.
In the prior art lifter assemblies, the top mounting plate has a linear actuator cylinder centrally located for lifting the mounting plate, and the pairs of shafts have generally supported base and intermediate plates, where the base plate is slidably attached to a first pair of shafts by a first pair of housings having bearings to slidingly support the shafts, while the intermediate plate is slidably attached to the second pair of shafts by a second set of housings and their respective bearings. This has created three distinct problems for modern manufacturing plants.
First, the prior art lifter assemblies required sufficient physical space for both the upward stroke and the bottom stroke of the lifter plate and rods for the lifter assembly. Although attempts have been made to solve this space problem, see for example U.S. Pat. No. 5,690,315, in which two pair of substantially parallel shafts are provided wherein one pair of shafts has the top mounting plate connected to the top of the shafts, while the bottom of the shafts are connected to a separate cross support member, which is, in turn, connected to yet another set of shafts, bearings and all the other necessary parts. This meant that the '315 compact lifter assembly did not require the shafts connected to the top mounting plate to extend beyond the bottom of the lifter assembly, thereby solving the problem of the required sufficient physical space for both the upward and bottom strokes. However, the '315 patent does not address the second and third problems that were presented by the prior art devices.
The second problem presented is that these lifter assemblies are used in very dirty environments, and any shavings, weld flash, or the like which are the by-products of the manufacturing operation, can become embedded directly in the bearings, scratching the cylindrical surface of the shaft, or the particles can become embedded in the lubricant used around the shafts and then be dragged into the bearings, causing great harm to the overall system. Traditionally, the lifter assemblies have taken up such a large "footprint" in the plants, that an enclosure to alleviate this problem has been impractical. The reason that the enclosure was not possible is that a constant ratio is needed for direct and constant contact between the actuating cylinder and the moving mounting plate in order to keep the closed dimension of the lifter kept at a constant, in addition to the necessity for keeping the stroke plus bearing ratio constantly engaged. Once these ratios are kept constant, the total workings of the lifter may be enclosed within a tolerably sized sheet metal guard to prevent outside contaminants from entering the enclosed space, thereby preventing harm to the inner workings. As one can imagine, it would be a real advantage to provide an enclosure over the entire unit, both in the retracted as well as the extended positions, such that the working mechanisms are protected from the working environment atmospheric impurities.
Moreover, a third problem arose in the prior art assemblies in that the conventional two post lifters actually included four posts, rather than two, to allow for the size of the lifter in an attempt to provide a sure and direct path for the shafts to permit reliable lifting and positioning of the workpiece. It would be a great advantage to the art to be able to actually only have two posts in a "two post" lifter as additional costs to the customer would be alleviated. The prior art four post "two post" lifters needed all four posts in order to have the two additional guide posts or shafts to allow for the size of the lifter in a closed state to be contained in the least amount of space. Furthermore, the additional posts or shafts were necessary to prevent deflection in position and path because the first set of shafts did not support the cylinder in the extended position. The additional number of shafts merely added to the problem of environment dirt contamination because there were twice as many shafts that could have problems.
Therefore, it would be a great advantage to the compact lifter if a new compact lifter could be discovered that would alleviate the space problem, prevent contaminants from entering the machinery, and merely utilize two posts, rather than four or six, for a "two post" lifter.